1. Field of the Invention
This invention relates to coating compositions for glass fibres, more particularly glass fibres which are intended for use as reinforcement in cement products, and is related to the invention described and claimed in U.S. Pat. No. 3,958,490 and application Ser. No. 646,785, assigned to the same assignee as the present invention.
2. Description of the Prior Art
In the alkaline environment of a normal Portland cement, which is mainly due to the presence of lime (calcium hydroxide), fibres of generally available glass compositions, such as that widely known as E-glass, are rapidly attacked and weakened so that the additional strength imparted to the cement by the glass fibres is rapidly lost.
Various alkali-resistant glass compositions have been devised which retain their strength better in cement.
Thus British patent specification No. 1,200,732 (National Research Development Corporation) describes and claims a composite fibre/cementitious product comprising fibrous reinforcing material distributed throughout a cement matrix, in which the reinforcing material is primarily a glass having per se a degree of alkali resistance such that when tested in the form of an abraded fibre of length 21/2 inches and a diameter of from 0.4 to 1.0 .times. 10.sup.-3 inches said fibre has a tensile strength of at least 100,000 p.s.i. after treatment with saturated aqueous Ca(OH).sub.2 solution at 100.degree. C for 4 hours followed by successive washings at ambient temperature with water, then with aqueous hydrochloric acid (1%) for 1 minute, water, acetone, followed by drying, said fibre experiencing not more than 10% reduction in diameter during said test.
British patent specification No. 1,243,972 (N.R.D.C.) discloses and claims such composite fibre/cementitious products in which the glass contains at least 65% SiO.sub.2 and at least 10% ZrO.sub.2 by weight. British patent specification No. 1,243,973 (N.R.D.C.) discloses and claims alkali-resistant glass fibres derived from a glass containing, in weight percentages, 65 - 80% SiO.sub.2, 10 - 20% Zro.sub.2 and 10 - 20% of a network modifier which is an alkali metal oxide, an alkaline earth metal oxide or zinc oxide, said glass being one which has a tensile strength as set out above.
Further ranges of glass compositions for forming alkali-resistant glass fibres are disclosed and claimed in our British Patent Specifications Nos. 1,290,528 and 1,389,019. Patent No. 1,290,528 claims glass compositions for forming glass fibres which are to be incorporated as reinforcement in cementitious products, comprising, in molecular weight percentages:
SiO.sub.2 : 62% to 75% PA1 ZrO.sub.2 : 7% to 11% PA1 R.sub.2 o: 13% to 23% PA1 R'o: 1% to 10% PA1 Al.sub.2 O.sub.3 : 0% to 4% PA1 B.sub.2 o.sub.3 : 0% to 6% PA1 Fe.sub.2 O.sub.3 : 0% to 5% PA1 CaF.sub.2 : 0% to 2% PA1 TiO.sub.2 : 0% to 4% PA1 SiO.sub.2 : 67 to 82 PA1 ZrO.sub.2 : 7 to 10 PA1 R.sub.2 o: 9 to 22.5 PA1 F.sub.2 : 3 to 9 PA1 Al.sub.2 O.sub.3 : 0 to 5 PA1 (computed as AlO.sub.1.5) PA1 i. increasing the efficiency of use of the polyhydroxy aromatic compound by reducing loss of the polyhydroxy compound from the fibre surface during manufacture of the cementitious product; this loss has been found to be evident in such products made without the resole resin by spray-up techniques and would be extensive in such products made using the pre-mix techniques. PA1 ii. reducing the retardant effect which the polyhydroxy aromatic compound has been found to exert on the setting characteristics of the cement. PA1 iii. (resulting from (ii) improving the early development of strength of glass-reinforced cement composite materials made with the coated fibres. PA1 a. Mono-cyclic 6-membered-ring aromatic compounds having at least three hydroxy groups substituted in the ring, e.g. PA1 b. Mono-cyclic 6-membered-ring aromatic compounds having at least three hydroxyl groups and at least one other group substituted in the ring, and carboxylic acid salts and esters thereof, e.g. PA1 c. Products obtained by oxidation of compounds of classes (a) and (b) in alkaline solution, e.g. PA1 d. A hetero-mono-cyclic 6-membered-ring aromatic compound having at least two nitrogen atoms within the ring and at least three hydroxyl groups as substituents in the ring, e.g. PA1 e. A polycyclic aromatic hydrocarbon having at least three hydroxyl groups substituted into a single 6-membered ring, e.g. PA1 a. the protective material's solubility in the carrier material used, PA1 b. the protective material's solubility in calcium hydroxide solution, and coupled with this the effectiveness of the particular compound being considered in reducing the rate of deterioration of the glass fibres in a cement matrix. Thus a compound of high effectiveness with a low solubility in calcium hydroxide solution may be effective at the same concentration as a compound of low effectiveness with high solubility in calcium hydroxide solution, PA1 c. the cost of the protective material used. It may be economically more desirable to use less of a more effective high cost compound, than a larger quantity of a less effective lower cost compound, PA1 d. the quantity of coating composition being picked up on the fibre during the coating process, which will determine the actual quantity of protective material present at the interface between the glass fibre and the cement matrix, PA1 e. the relative reactivity of the protective material with the phenolic resin present in the coating composition under chosen drying conditions.
wherein R.sub.2 O represents Na.sub.2 O, up to 2 mol.% of which may be replaced by Li.sub.2 O, and R'O is an oxide selected from the group consisting of the alkaline earth metal oxides, zinc oxide (ZnO) and manganous oxide (MnO), the balance if any consisting of other compatible constituents.
U.S. Pat. No. 1,389,019 claims glass compositions for forming into alkali-resistant continuously-drawn glass fibres, comprising in molar percentages on the oxide basis:
the balance, if any, consisting of other compatible constituents, where R = Na, up to 5 mol.% of which may be replaced by Li or K, and fluorine is included in substitution for oxygen in one or more of the oxides, the maximum value of the molar percentage represented by SiO.sub.2 + ZrO.sub.2 + AlO.sub.1.5 being dependent linearly on the content of both ZrO.sub.2 and F.sub.2, ranging, when F.sub.2 = 9 mol.%, from 89 mol.% when the ZrO.sub.2 content is 7 mol.% to 88 mol.% when the ZrO.sub.2 content is 8.5 mol.%, down to 87 mol.% when the ZrO.sub.2 content is 10 mol.%, the said maximum value being reduced by a further 5 mol.% over the whole scale when F.sub.2 = 3 mol.%.
U.S. Pat. No. 3,840,379 (Owens-Corning Fiberglas Corporation) describes another range of alkali-resistant glasses, and glass fibres made from them, having compositions within the following range:
______________________________________ Weight Percent Mol.Percent ______________________________________ SiO.sub.2 60 to 62 65 to 67 CaO 4 to 6 4.5 to 6.5 Na.sub.2 O 14 to 15 14.5 to 16 K.sub.2 O 2 to 3 1 to 2.5 ZrO.sub.2 10 to 11 5 to 6 TiO.sub.2 5.5 to 8 4.5 to 6.5 ______________________________________
Although alkali-resistant glass fibres as described in the above Patent Specifications retain their strength in cement much better than fibres of conventional glasses, such as E-glass, there is nevertheless, a gradual deterioration over long periods.
When producing glass fibres for any purpose, it is normal practice to coat the individual, continuously-drawn glass fibres, immediately after drawing, with a size composition which provides a mechanical protection and a lubricant for the fibres to minimise breakage and abrasion during the subsequent processing, namely the bringing together of numerous individual fibres to form a strand and the winding of the strand on a spool or drum. The size compositions previously used on glass fibres to be included in a cementitious matrix do not have any material effect on the long term resistance of the glass to attack by the alkalis in cement.
Protective coating compositions have also been applied to glass fibres at various stages in their production and processing, and it has, for example, been proposed to use a furane resin in such a coating for increasing the alkali resistance of the glass fibre material to render it suitable for use in reinforcing concrete.
U.S. Pat. No. 3,954,490 describes a composition for coating glass fibres intended for use as reinforcement in cementitious products, containing, as a protective material, at least one monocyclic or polycyclic aromatic compound which has at least three hydroxyl groups on the aromatic ring or (in a polycyclic compound) on at least one of the aromatic rings, said composition, when applied to a strand of glass fibres which is subsequently encased in a block of ordinary Portland cement paste which is allowed to cure and kept for 28 days in water at 50.degree. C, producing an improvement of at least 10% in the tensile strength of the strand as compared with that of a strand similarly treated and tested but without application of said composition.